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As in osmosis the pricipal factor
that influences the osmotic pressure is the ratio
of the solute to water molecules within the
solution.
Thus in comparison to molarity
which is defined as the number of moles of solute
dissolved in one litre of solution, molality
is described as the number of moles of the solute
dissolved in one kilogram of water.
Osmolality reflects
the number of moles of osmotically active
particles in one kilogram of water.
Thus one mole of glucose in one
kilo of water has an osmolality of 1 Osmol/Kg
while one mole of sodium chloride in one kilo of
water has an osmolality of 2 Osmol/Kg as each
mole of sodium chloride gives two moles of
osmotically active particles in solution.
Though the accurate measurement is
of osmoles per kilo, in actual fact iot is
difficult ot assess the mass of water in an
enclosed body.
On the other as the difference
between osmoles per kilo and osmoles per litre
for dilute solutions and given the fact that most
of the body fluids are dilute solutions,
osmolarity (osmoles/litre) is usually utilised
for physiological purposes.
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